(1) Field of the Invention
This invention relates to an electrophotographic plate, and more particularly to a high-sensitivity electrophotographic plate having a photosensitive layer containing an organic photoconductive material.
(2) Description of the Prior Art
Heretofore, inorganic photoconductive materials such as selenium, cadmium sulfide and zinc oxide have been popularly used for the photosensitive layer of the electrophotographic plates. Studies on use of organic photoconductive materials for the photosensitive layer of the electrophotographic plates have advanced rapidly in recent years, and some of such studies have materialized into practical use. The organic photoconductive materials have many advantages over the inorganic ones, for example the former is light in weight and easy to fabricate as a film and can also be easily manufactured into a sensitive plate, even a transparent sensitive plate in the case of using certain kinds of such organic materials.
Many studies have been made on the photoconductive polymers including polyvinylcarbazole, but these polymers are not always satisfactory in certain respects such as film-forming properties, flexibility and adhesiveness, and when these polymers are formed into a thin film, such film tends to develop cracks or separate from the substrate. Additives such as plasticizer, binder, etc., are added to eliminate said defects, but addition of such additives gives rise to additional problems such as reduced sensitivity and increased residual potential. Thus, it was very difficult to obtain a practical sensitive plate comprising organic photoconductive materials.
On the other hand, the low-molecular organic photoconductive compounds allow easy production of a sensitive plate with excellent mechanical properties because such compounds permit selection of a polymer with excellent film-forming properties, flexibility, adhesiveness and other properties as binder, but it was difficult to find out a compound suited for making a high-sensitivity plate.
In view of the above, the present inventors have pursued further research into the organic low-molecular photoconductive compounds capable of providing a high-sensitivity, high-durability electrophotographic plate and, as a result, found that certain specified hydrazone compounds are best suited for the purpose envisaged. This invention was reached on the basis of such finding.